the only thing that I would think of off hand is a possible issue with the wire from the fuses to the pump...since you've tested and know the pump works if you bypass and jump straight from the battery. but, I'm no expert

Only thing that is bothering me is that the second pump is used from a less than reputable salvage yard. They had already purchased the pump and then asked me to install it.

But you tested both pumps with B+ directly & they activate so I think you covered that. Since pump fuse 25 was blown at the onset, I have to suspect a harness issue. Yet you say that has checked out too. Is there fuel in the tank? Maybe the pump has an automatic cutoff (unsure). You have checked the ground for high resistance? You are using a multimeter & not a continuity checker.

12 volts doesn't mean much, will it light a high amp bulb. If not poor connection, no amperage.

I just went and load tested the circuit with an old 75w off road light and it lights bright. Also did a continuity test on the gray power wire and black ground all the way from the fuse box to the tank and they checked out good.

I just went and load tested the circuit with an old 75w off road light and it lights bright. Also did a continuity test on the gray power wire and black ground all the way from the fuse box to the tank and they checked out good.

Continuity is not very helpful. You can have good continuity & very high resistance simultaneously.

I have not worked on these circuits in a long time but GM used to switch all their computer controlled circuits except fuel pump by supplying constant ignition voltage and switching the ground side. The fuel pump at that time (early 90's) was switched 12v for safety. If you are able to light the lamp on the gray wire anytime the ignition is on then they switched to controlling the fuel pump by switching ground on and off. The up shot is a bad connection at the PCM or heaven forbid the blown fuse event took out the power transistor in the PCM, the power transistor is supposed to be protected but may not always work. YMMV as I have not looked at a wiring diagram for this vintage car yet, I just finally moved out of the 1990's by buying this 2009 G6.

In the G6 there is a constant ground, when the ignition is turned on the PCM send power to the relay which then allows power to the pump for 2 - 3 seconds to prime it and then shuts off power if the computer does not detect ignition. So it's still about the same as the 90's.

Both of the vehicles I own are from the 90's too, much easier to work on. lol.

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